Clinical course and pathogenicity of variant rabbit haemorrhagic disease virus in experimentally infected adult and kit rabbits: Significance towards control and spread

RHDVb has become the dominant RHDV on the Iberian Peninsula. A better understanding of its pathogenicity is required to aid control measures. Thus, the clinical course, humoral immune response, viraemia and kinetics of RHDV-N11 (a Spanish RHDVb isolate) infection in different tissues at both viral RNA and protein levels were studied in experimentally infected young and adult rabbits. The case fatality rate differed between the two age groups, with 21% of kits succumbing while no deaths were observed in adults. Fever and viremia were strongly associated with death, which occurred 48 h post infection (PI) too fast for an effective humoral immune response to be mounted. A significant effect on the number of viral RNA copies with regard to the variables age, tissue and time PI (p < 0.0001 in all cases) was detected. Histological lesions in infected rabbits were consistently more frequent and severe in liver and spleen and additionally intestine in kits, these tissues containing the highest levels of viral RNA and protein. Although no adults showed lesions or virus antigen in intestine, both kits and adults maintained steady viral RNA levels from days 1 to 7 PI in this organ. Analysis revealed the fecal route as the main dissemination route of RHDV-N11. Subclinically infected rabbits had detectable viral RNA in their faeces for up to seven days and thus may play an important role spreading the virus. This study allows a better understanding of the transmission of this virus and improvement of the control strategies for this disease.

Conventional and real time RT-PCR assays for the detection and differentiation of variant rabbit hemorrhagic disease virus (RHDVb) and its recombinants

Since its emergence, variant RHDV (RHDVb/RHDV2) has spread throughout the Iberian Peninsula aided by the apparent lack of cross protection provided by classic (genogroup 1; G1) strain derived vaccines. In addition to RHDVb, full-length genome sequencing of RHDV strains has recently revealed the circulation of recombinant viruses on the Iberian Peninsula. These recombinant viruses contain the RHDVb structural protein encoding sequences and the non-structural coding regions of either pathogenic RHDV-G1 strains or non-pathogenic (np) rabbit caliciviruses. The aim of the work was twofold: firstly to validate a diagnostic real time RT-PCR developed in 2012 for the detection of RHDVb strains and secondly, to design a conventional RT-PCR for the differentiation of RHDVb strains from RHDVb recombinants by subsequent sequencing of the amplicon.

Lambs are Susceptible to Experimental Challenge with Spanish Goat Encephalitis Virus

Spanish goat encephalitis virus (SGEV) is a member of the genus Flavivirus, family Flaviviridae, and causes encephalomyelitis in goats. The aim of this study was to determine whether sheep are susceptible to experimental challenge with SGEV by two different routes. The results show that SGEV can infect sheep by both the subcutaneous and intravenous routes, resulting in neurological clinical disease with extensive and severe histological lesions in the central nervous system. Lambs challenged subcutaneously developed more severe lesions on the ipsilateral side of the brain, but the lesion morphology was similar irrespective of the route of challenge. The clinical presentation, pathogenesis, lesion morphology and distribution shows that SGEV is very similar to louping ill virus (LIV) and therefore any disease control plan must take into account any host species and SGEV vectors as potential reservoirs. Furthermore, discriminatory diagnostics need to be applied to any sheep or goat suspected of disease due to any flavivirus in areas where SGEV and LIV co-exist.

Fast specific field detection of RHDVb

This work describes a simple and rapid test for field detection of the emerging rabbit pathogen RHDVb. The assay is specific for RHDVb, showing no cross-reactivity with other RHDV types giving a specific result in under 10 min using rabbit liquid exudates or liver homogenate samples taken at necropsy.

Complete genome sequence of two rabbit hemorrhagic disease virus variant b isolates detected on the Iberian Peninsula

We report the complete genome sequences of two isolates (RHDV-N11 and CBVal16) of variant rabbit hemorrhagic disease virus (RHDVb). Isolate N11 was detected in young domestic animals during a rabbit hemorrhagic disease (RHD) outbreak that occurred in 2011 on a rabbit farm in Navarra, Spain, while CBVal16 was isolated from a wild rabbit found dead in Valpaços, Northern Portugal, a year later. The viral sequences reported show 84.8-85.1 % and 78.3-78.5 % identity to RHDVAst/89 and RCV-A1 MIC-07, representative members of the pathogenic genogroup 1 RHDV and apathogenic rabbit calicivirus, respectively. In comparison with other RHDV isolates belonging to the previously known genogroups 1-6, RHDVb shows marked phenotypic differences, as it causes disease preferentially in young rabbits under 40 days of age and shows modified red blood cell agglutination profiles as well as antigenic differences that allow this variant to escape protection by the currently available vaccines.

Vesicular stomatitis virus glycoprotein containing the entire green fluorescent protein on its cytoplasmic domain is incorporated efficiently into virus particles

The envelope glycoprotein (G) of vesicular stomatitis virus (VSV) contains a short cytoplasmic domain of 29 amino acids. To determine whether VSV particle assembly could accommodate a G protein with a large cytoplasmic domain, we constructed a gene called G/GFP encoding the VSV G protein with the 27-kDa green fluorescent protein linked to its cytoplasmic domain. This gene was inserted into the infectious clone of VSV and we recovered a recombinant virus expressing G/GFP from this extra gene. This VSV-G/GFP virus grew to titers equivalent to that of wild-type virus and was stable upon passaging. The G/GFP protein formed mixed trimers containing an average of two wild-type G proteins and one G/GFP protein. This heterotrimeric protein was expressed on the cell surface, and was incorporated into virus particles with almost the same efficiency as wild-type VSV G protein. These results indicate that there is substantial space available between the viral membrane and the nucleocapsid that can accommodate such a large cytoplasmic domain. The green fluorescent virus particles were readily visualized by fluorescence microscopy and had a normal morphology by electron microscopy. To determine whether virus assembly could occur efficiently when all G proteins contained the GFP cytoplasmic domain, a VSV recombinant in which the G gene was completely replaced by the VSV-G/GFP gene was recovered. This virus rapidly lost expression of the GFP protein sequence through introduction of a stop codon within the sequence encoding the G cytoplasmic domain, indicating strong selection against homotrimeric G protein bearing such a large cytoplasmic domain.